so you can use SJMP or ACALL as previously mentioned, but always end the SJMP with the RETI. and the ACALL with a RET and then in the ISR a RETI. (Is this required??)

I didn't see where anybody mentioned using ACALL, but if you were to use one, then yes, the RET followed sometime later by RETI is required. The vectoring of the interrupt itself performed an implicit CALL (pushing the first return address), then if you do an ACALL (pushing a second return address), two returns are required. One of the returns should be of the RETI variety to clear that interrupt's "priority level active" flip-flop. There are nuances you should be aware of if you care to RETI then RET, and if you'd want to do it that way, you have undoubtedly already read the '51 architecture documents to know why.